DGLA (8,11,14-eicosatrienoic acid) is one of the constituent fatty acids in fish oils, marine algae and the like. DGLA is known to be produced as a precursor for arachidonic acid (also referred to hereinafter as ARA) in microbes such as Mortierella alpina. However, there is only a slight amount of generation of DGLA in microbes containing triglycerides, diglycerides, monoglycerides, phospholipids and sterols as lipid components. DGLA and ARA are fatty acids that have similar chemical characteristics. Thus, separation of DGLA from ARA is difficult.
Technology has been proposed for decreasing the generated amount of ARA in the microbe in order to produce DGLA in an efficient manner.
For example, Japanese Patent Application Laid-Open (JP-A) No. H5-091887 discloses a method of producing DGLA or a lipid containing DGLA, the method comprising culturing a microbe having an ability to produce arachidonic acid but having a reduced or lost Δ5 desaturation activity, to produce DGLA or DGLA-containing lipids, and recovering the DGLA or DGLA-containing lipids. JP-A No. H-091887 also discloses that the microbe having an ability to produce arachidonic acid and having a reduced or lost Δ5 desaturation activity is cultured in the presence of a Δ5 desaturase inhibitor, e.g. sesamin or the like.
Moreover, WO 2005/083101 discloses a method of producing phospholipid containing a long-chain polyunsaturated fatty acid such as arachidonic acid and DGLA as a constituent component. The method comprises steps of extracting phospholipids from defatted cells obtained by extracting oils/fats containing triglycerides from cells of a lipid-producing microbe, which microbe produces a lipid containing a long-chain polyunsaturated fatty acid as a constituent component.
Despite these prior disclosures, commercial production of DGLA-rich microbial oil has scarcely taken place up to now, because of the technical difficulties in achieving a product of satisfactory and useful quality.